There are many beautiful shells you can find along our WA coastline. From the large shells of the giant clam to the common pipi shell, to the iconic cowrie which is often used in jewellery, there are a diverse range of beautiful shells to be found at the beach.

Where Do Shells Come From?

All shells once belonged to a living animal, most of them once belonging to a marine mollusc – a large group of animals, comprising of about 23% of all named marine organisms! A shell is the exoskeleton of these animals, formed to protect their delicate bodies from predators and the elements. There are 7 classes of molluscs, however bivalves and gastropods are two of the larger classes and are some of the most common shells you see washed up on the beach.

Bivalves

A bivalve has a double hinged shell, such as a scallop, clam, mussel and oyster. There are over 15,000 species, and do not have a distinct head or radula. Majority of these animals are filter feeders, using a modified gill to remove food particles from the water, such as phytoplankton, bacteria, small crustaceans and algae.

Gastropods

Gastropods are the largest group in the phylum Mollusca, with around 65,000 animals belonging to this class. They are characterised by a single, often coiled shell or no external shell at all, a ventral muscular foot and a distinct head, such as snails, cowries, limpets, abalone and slugs.

Roe’s abalone

How do they make their shells?

So how do these soft, slimy creatures make these beautiful, striking shells? Shells are made mostly from calcium carbonate, one of the most abundant minerals on Earth. Specialised cells in the mantle (skin) secrete protein and minerals, with proteins making up around 2% of the shell. These proteins set the framework that determine which minerals are used in the formation of the shell and provides support. A mollusc’s mantle absorbs salt and other minerals/chemicals from the marine environment around them, which they are then able to secrete as calcium carbonate that makes up most of the shell. Seashells vary so much to meet the needs of the specific animal, with each species having varying behaviours, habitats and diets. For example, molluscs with a wider variety of food sources often have a range of different pigments, which results in more colourful shells. On the other hand, molluscs who live in cold water with limited food choices tend to grow shells in more solid, dark colours. Shells continue to grow as the animal inside it grows, with some shells even displaying seasonal growth lines that can indicate how old it was when it died!

Look, but don’t take

While these shells may seem like a treasure to find along the beach, it is very important to not take anything from a marine park or with a living creature inside. Empty shells provide shelter for a range of marine life, including hermit crabs which cannot make their own shells like molluscs. Shells are also important part of recycling calcium carbonate back into the ecosystem and beach stability by reducing erosion and absorbing wave energy.

Did you know?

Have you ever found a shell on the beach with what looks like a neatly drilled hole in it? This hole may have been created by a predatory snail. When they find small shells like pipis in the surf zone, they will use their radula to force their way into the pipis shell and feed on its body.